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Inverters and AC motors

H

hamilton

Jan 1, 1970
0
With the current discussion of inverters and an electric blankeypoo,

I would like to create a backup for the Gas-Forced-Air furnace in my house.

The last time the power went out, the gas stove still had gas flowing.

But with the power out, the furnace would not work.

So, will a Pure Sine Wave inverter be able to run the motor in a
standard furnace ?

Thanks

hamilton
 
C

Cydrome Leader

Jan 1, 1970
0
hamilton said:
With the current discussion of inverters and an electric blankeypoo,

I would like to create a backup for the Gas-Forced-Air furnace in my house.

The last time the power went out, the gas stove still had gas flowing.

But with the power out, the furnace would not work.

So, will a Pure Sine Wave inverter be able to run the motor in a
standard furnace ?

It should.

furnace blowers are just plain capacitor run induction motors, with no
crazy starting coils, so there's not a need for a hugely oversized
inverter.
 
P

P E Schoen

Jan 1, 1970
0
"hamilton" wrote in message
With the current discussion of inverters and an electric blankeypoo,
I would like to create a backup for the Gas-Forced-Air furnace in my
house.
The last time the power went out, the gas stove still had gas flowing.
But with the power out, the furnace would not work.
So, will a Pure Sine Wave inverter be able to run the motor in a standard
furnace ?

You might not even need a pure sine wave. I was able to run a 1/2 to 3/4 HP
pump motor on a 2000W Harbor Freight "modified sine wave" inverter that cost
only about $100. I was also able to run a 2 HP three phase motor using a
400W inverter and a voltage doubler to provide DC bus voltage for a VFD
(which I had purchased new for about $60). And recently I bought a 1000W 220
VAC inverter for about $40 and hooked it directly to two of the AC inputs of
the VFD and the motor runs just fine, although I'm not sure how much load it
will take. I might hack the inverter and access the internal DC bus which is
probably about 300 VDC and perfect for the VFD's DC link.

You might even consider a bank of 20-30 smaller 12V batteries in series to
get the DC link voltage directly. I bought some 12V 12Ah SLAs on eBay for a
little over $22 each, so for about $500 you can have 3.6 kWh capacity which
should run a 1/4 HP (200W) furnace fan for about 12-15 hours total. Of
course, you can also get 12V 100Ah flooded lead batteries for less than $100
each.

http://www.ebay.com/itm/320800175307 (1000W 220V inverter)
http://www.ebay.com/itm/190701779364 (12V 12Ah batteries)
http://www.ebay.com/itm/190750912593 (small VFD $50)
http://www.ebay.com/itm/180906231025 (110V 2.2 kW single phase VFD)

Paul
 
G

gregz

Jan 1, 1970
0
Cydrome Leader said:
It should.

furnace blowers are just plain capacitor run induction motors, with no
crazy starting coils, so there's not a need for a hugely oversized
inverter.

I don't know how much power mine takes, but it must have 16 wires going to
the variable speed motor. Also makes a lot of RFI. I don't see me using an
inverter but who knows.

Just got to hooking up my solar panels.

Greg
 
C

Cydrome Leader

Jan 1, 1970
0
P E Schoen said:
"hamilton" wrote in message





You might not even need a pure sine wave. I was able to run a 1/2 to 3/4 HP
pump motor on a 2000W Harbor Freight "modified sine wave" inverter that cost
only about $100. I was also able to run a 2 HP three phase motor using a
400W inverter and a voltage doubler to provide DC bus voltage for a VFD
(which I had purchased new for about $60). And recently I bought a 1000W 220
VAC inverter for about $40 and hooked it directly to two of the AC inputs of
the VFD and the motor runs just fine, although I'm not sure how much load it
will take. I might hack the inverter and access the internal DC bus which is
probably about 300 VDC and perfect for the VFD's DC link.

furnaces have overly complex micro controlled nonsense in them these
days, so not blowing out the electronics might be a consideration, over
the older furnaces with a relay, gas valve and thermocouple wired to a
thermostat.

OP has a complex sounding motor too- are they no longer using one or two
speed fan motors?
 
H

hamilton

Jan 1, 1970
0
You will need to dream up some switchover scheme that still meets code.

My thoughts on switch over is very very simple, manual switch over.

Re-wire the furnace romex with a three prong plug/outlet.

Plug the furnace into the three prong outlet.

When the power goes out, un-plug the furnace for Public Service and plug
into the inverter.
And those AGM batteries are not to compact. But they are good exercise
to move around.

From a project for a battery based APU, the Odyssey batteries turned

I will look at Odyssey.

Thanks

hamilton
 
S

Sylvia Else

Jan 1, 1970
0
"hamilton" wrote in message





You might not even need a pure sine wave. I was able to run a 1/2 to 3/4
HP pump motor on a 2000W Harbor Freight "modified sine wave" inverter
that cost only about $100. I was also able to run a 2 HP three phase
motor using a 400W inverter and a voltage doubler to provide DC bus
voltage for a VFD (which I had purchased new for about $60). And
recently I bought a 1000W 220 VAC inverter for about $40 and hooked it
directly to two of the AC inputs of the VFD and the motor runs just
fine, although I'm not sure how much load it will take. I might hack the
inverter and access the internal DC bus which is probably about 300 VDC
and perfect for the VFD's DC link.

I once tried running a simple house fan on a modified sine way. Apart
from a buzzing noise, it seemed OK, until the smell indicated that it
was overheating. Presumably it didn't like the higher harmonic currents
that were flowing.

The message here being that the first indication you get that running
with a modified sine way isn't a good idea may be that the motor stops -
permanently.

Sylvia.
 
H

hamilton

Jan 1, 1970
0
I once tried running a simple house fan on a modified sine way. Apart
from a buzzing noise, it seemed OK, until the smell indicated that it
was overheating. Presumably it didn't like the higher harmonic currents
that were flowing.

The message here being that the first indication you get that running
with a modified sine way isn't a good idea may be that the motor stops -
permanently.

Sylvia.
Thank You Sylvia,

This is the kind of information I am looking for.

hamilton
 
J

josephkk

Jan 1, 1970
0
It should.

furnace blowers are just plain capacitor run induction motors, with no
crazy starting coils, so there's not a need for a hugely oversized
inverter.
Just the same it has to be motor rated. It has to be robust enough to
handle a couple of seconds of 10X rated current. Cap run does not fix
that.

?-)
 
J

josephkk

Jan 1, 1970
0
apacitor run induction motors, with no

I don't know how much power mine takes, but it must have 16 wires going to
the variable speed motor. Also makes a lot of RFI. I don't see me using an
inverter but who knows.

Sounds like a poorly implemented variable frequency drive.

?-)
 
G

gregz

Jan 1, 1970
0
josephkk said:
Just the same it has to be motor rated. It has to be robust enough to
handle a couple of seconds of 10X rated current. Cap run does not fix
that.

?-)

I just checked the current on my furnace with variable speed motor. The
motor uses a whole bunch of wires with switching control. Not much current
for exhaust and ignitors. Ramps slowly up to just under 3 amps 120 vac. Im
not sure if it increases a bit if it goes into full btu mode. It's also a
dual 50k 70k btu burner.
Yes, I'm hooking my solar system, 6 panel harbor freight and just got a 1kw
sine inverter. I have not hooked everything up, but I was impressed on 3
panels delivering current on a cloudy day. I'll be taking more
measurements. I didn't intend on using the inverter on furnace, but looks
promising. Still got 3 gas generators. 1kw, 3.5 kw, 5kw .

Greg
 
J

josephkk

Jan 1, 1970
0
I just checked the current on my furnace with variable speed motor. The
motor uses a whole bunch of wires with switching control. Not much current
for exhaust and ignitors. Ramps slowly up to just under 3 amps 120 vac. Im
not sure if it increases a bit if it goes into full btu mode. It's also a
dual 50k 70k btu burner.

Maybe you have a high grade furnace with a VFD. How old is it? If it is
more than 10 years old VFD is very unlikely. Two or three speed can be
done with multiple windings with different pole counts (ceiling fans).
 
C

Cydrome Leader

Jan 1, 1970
0
josephkk said:
Just the same it has to be motor rated. It has to be robust enough to
handle a couple of seconds of 10X rated current. Cap run does not fix
that.

they're just boring fan motors, no starting coils and they're not even all
that powerful, so the inrush current won't be all that exciting. If I get
bored this weekend I'll take some current readings off one (entire blower
assembly from a furnace.)
 
G

gregz

Jan 1, 1970
0
josephkk said:
Maybe you have a high grade furnace with a VFD. How old is it? If it is
more than 10 years old VFD is very unlikely. Two or three speed can be
done with multiple windings with different pole counts (ceiling fans).

It's 6 years old. Goodman.

Greg
 
L

Les Cargill

Jan 1, 1970
0
Phil said:
On Fri, 16 Nov 2012 23:28:40 +0000 (UTC), Cydrome Leader

[snip]
they're just boring fan motors, no starting coils and they're not
even all
that powerful, so the inrush current won't be all that exciting. If I
get
bored this weekend I'll take some current readings off one (entire
blower
assembly from a furnace.)

I've been musing over the problem of lack of heat for so many homes in
the aftermath of Hurricane Sandy.

It seems almost a trivial problem to make a natural-gas-powered
blower, then furnaces work even when electricity is lost.

...Jim Thompson

But not thermostats or water pumps or lights. I've been considering a
natural gas powered standby generator for some time, but our lights
usually go back on within a day, which makes such a beast a very
expensive luxury. Cool though.

Cheers

Phil Hobbs


I've known a couple of people who did this:
http://www.propane-generators.com/type_3.htm

One was basically enough to run the 'fridge, freezer, and a few lights.
It was an otherwise stock gasoline generator. In both cases,
an inspection was done by a licensed plumber ( always a great idea when
messing with natural gas ).
 
T

tm

Jan 1, 1970
0
Jim Thompson said:
On Fri, 16 Nov 2012 23:28:40 +0000 (UTC), Cydrome Leader

[snip]

they're just boring fan motors, no starting coils and they're not even
all
that powerful, so the inrush current won't be all that exciting. If I
get
bored this weekend I'll take some current readings off one (entire
blower
assembly from a furnace.)


I've been musing over the problem of lack of heat for so many homes in
the aftermath of Hurricane Sandy.

It seems almost a trivial problem to make a natural-gas-powered
blower, then furnaces work even when electricity is lost.

...Jim Thompson

But not thermostats or water pumps or lights. I've been considering a
natural gas powered standby generator for some time, but our lights
usually go back on within a day, which makes such a beast a very
expensive luxury. Cool though.

Cheers

Phil Hobbs

Once upon a time, ~1970, it was actually cheaper, in Arizona, to run a
gasoline powered VW engine driving a generator, than to buy
electricity from Arizona Public Service. One of my technicians did
just that for a cabin too far from distribution.

And we ran all the costs including maintenance.

...Jim Thompson
--

Iff you can recover the waste heat from a natural gas powered generator and
use that for space heating, the efficiency gets crazy good. Trick would be
to level out the electrical demand with some form of battery storage and
conversion.
 
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